Introduction
The San Diego Center of Excellence in Diving at UC San Diego aims to help divers be effective consumers of scientific information through its “Healthy Divers in Healthy Oceans” mission. In this monograph we explore a research report from the Navy Experimental Diving Unit (NEDU) that is leading some divers to think they should be cold if they want to reduce decompression risk. That is a misinterpretation of the report, and may be causing divers to miss some of the joy of diving. There is no substitute for comfort and safety on a dive.

Background
In 2007 NEDU published their often-cited report “The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness” (Gerth et al., 2007). The authors, Drs. Wayne Gerth, Victor Ruterbusch, and Ed Long were questioning the conventional wisdom that cold at depth increases the risk of decompression illness. After conducting a very carefully designed experiment, they were shocked to find that exactly the opposite was true. Some degree of cooling was beneficial, as long as the diver was warm during ascent.

Discussion and Implications
There are some important caveats for the non-Navy diver to consider. First of all, it was anticipated that a diver would have a system for carefully controlling their temperature during the separate phases of bottom time and decompression. Most non-Navy divers do not have that sort of surface support.

Secondly, the “cold” water in the NEDU study was 80 °F (27 °C). For most of us, 80 °F (27 °C) is an ideal swimming pool temperature, not exactly what you are going to find in non-tropical oceans and lakes. The warm water was 97 °F (36 °C), also a temperature not likely to be available to recreational and technical divers.

When testing the effect of anything on decompression results, the Navy uses their extensive mathematical expertise to select the one dive profile that is, in their estimation, the most likely to identify a difference in decompression risk, if that difference in risk exists. In this case the profile selected was a 120 fsw (37 msw) dive with 25 to 70 min bottom time, decompressed on a US Navy Standard Air table for 120 fsw (37 msw) and 70 min bottom time. That table prescribes 91 minutes of decompression divided thusly: 30 fsw/9 min (9msw/9 min), 20 fsw/23 min (6 msw/23 min), 10 fsw/55 min (3 msw/55 min).

A total of 400 carefully controlled dives were conducted yielding 21 diagnosed cases of decompression sickness. Overwhelmingly, the lowest risk of decompression was found when divers were kept warm during decompression. The effects of a 9 °C increase in water temperature during decompression was comparable to the effects of halving bottom time.

That is of course a remarkable result, apparently remarkable enough to cause civilian divers to alter their behavior when performing decompression dives. However, before you decide to chill yourself on the bottom or increase your risk of becoming hypothermic, consider these facts.

Do you have a way of keeping yourself warm, for instance with a hot water suit, during decompression? If not, the study results do not apply to you.

Of the many possible decompression schedules, the Navy tested only one schedule, the one considered to be the best for demonstrating a thermal influence on decompression risk. Although it seems reasonable that this result could be extrapolated to other dive profiles, such extrapolation is always risky. It may simply not hold for the particular dive you plan to make, especially if that dive is deeper and longer than tested.

Most commercial decompression computers do not adhere to the U.S. Navy Air Tables; few recreational dives are square profiles. Furthermore, additional conservatism is usually added to commercial algorithms. NEDU is not able to test the effects of diver skin temperature on all proprietary decompression tables, nor should they. That is not their mission.

The scientific method requires research to be replicated before test results can be proven or generalized. However, due to the labor and expense involved in the NEDU dive series, it seems unlikely that any experiments that would determine the relevance of these results to recreational or technical diving will ever be performed. As such, it may raise as many questions as it answers. For instance, the original question remains; if you become chilled on a dive, how does that affect your overall risk of decompression illness compared to remaining comfortably warm? Unfortunately, that question may never be answered fully.

Thermoneutral temperatures for swim suited divers are reported to be 93 °F to 97 °F (34 to 36 °C) for divers at rest and 90 °F (32 °C) during light to moderate work (Sterba, 1993). So a skin temperature of 80 °F (27 °C) is indeed cold for long duration dives. If your skin temperature is less than 80 °F (27 °C), then you are venturing into the unknown; NEDU’s results may not apply.

In summary, beer and some types of wine are best chilled. Arguably, divers are not.

Acknowledgments
Support for the San Diego Center of Excellence in Diving is provided by founding partners UC San Diego Health Sciences, UC San Diego Scripps Institution of Oceanography, OxyHeal Health Group, Divers Alert Network, Diving Unlimited International, Inc. and Scubapro.

https://www.tdisdi.com/wp-content/uploads/2014/12/NEDU.jpg161300jamescouncillhttps://www.tdisdi.com/wp-content/uploads/2015/07/logo2.pngjamescouncill2014-12-16 09:20:582017-03-30 11:36:43Don't Dive Cold When You Don't Have To

As if cave diving isn’t challenging enough, how should we feel about adding a rebreather to the mix?

When asked, which happens from time to time, I’ll explain to anyone who’ll listen that the easiest way to really give your diving skills a workout is to enroll in a cave diving class. The customer feedback from folks, who take this piece of advice, and dive into a technical overhead program, usually makes extensive use of the words “humbling” and “embarrassing”. The phrase: “brought me down a peg” or something similar often makes an appearance too.

Cave diving, and to some extent Advanced Wreck Diving (i.e. wreck penetration), is fundamental to technical diving. Most of the information covered and the majority of skills and techniques taught in any technical diving program have their foundations in basic cave diving. The presence of a rock ceiling, rock walls, and a rock floor (often covered in a deep layer of fine-grained mud) tends to focus the mind and put a special meaning and strong emphasis to the sage advice that bailing out to the surface is not an option. As any technical diver will tell you, it’s very unwise to bolt for the surface on any dive, especially one that’s incurred a decompression obligation, but in a cave several hundred metres or feet from open water, that option is completely off the table. Problems of all shapes and sizes have to be fixed at depth.

One result of not being able to surface at will, is the cave diver’s conservative approach to gas management: specifically, carrying enough gas to get them and a buddy back to safety in the event of the most horrendous equipment malfunction at the back of the cave. The Rule of Thirds, the starting point from which cave divers traditionally begin their gas volume calculations, is the ubiquitous gas management technique adopted by virtually all technical divers.

Also, the techniques developed and refined by cave divers operating in North Florida and the Caribbean for communications, propulsion, equipment selection and configuration have to a great extent become the best-practice defaults for almost every technical diver around the world.

Furthermore, it’s long been accepted that the standards required for cave instructors (and their students) to earn their certifications to teach (or dive) in caves, are among the most stringent. Broadly speaking, the consensus is that cave divers and the men and women who certify them, are among the most meticulous and squared away of any group of divers.

So, what happens when we take the rigors of a cave diving course and apply them to a new program for which the core life-support systems have been changed from open-circuit to closed?

To begin any comparison, it’s fair to say that TDI’s training department and advisory panel thought long and hard about the best ways to evolve its successful cave diving curriculum to include the special needs of closed-circuit rebreather diving. I was not at head-office for the whole of the development process, but I know it was the work of a larger development team than any previous program. Which is hardly surprising given the magnitude of responsibility to “get it right” when combining the complexity of a rebreather with a supremely challenging underwater environment. Hardly surprising and somewhat comforting!

Given that, let’s look at what they came up with!

The basic shape of most cave courses is the same regardless of what type of gear the diver opts to use. The first step is Cavern Diver. Graduates from Cavern can move up to Intro-Cave Diver; and once that level is achieved are able to sign-up for Intro to Cave and Full Cave courses.

In the briefest of terms, cavern divers are severely limited in where they can venture; intro-cave divers have to stay on the permanent main line or gold line and are not allowed to make any jumps to side passages; and full-cave divers have a license to learn in most of the cave’s main and secondary passages.

The progression has stood almost unchanged since the first organised cave diving programs that pre-date the formation of most of today’s mainstream certifying agencies… in other words, it’s a progression that’s stood the test of time and held its value well. It then follows logically that TDI’s CCR Cave program follows this same structural paradigm.

WHAT’S A CAVERN?
I don’t think there’s any real confusion about where open water ends and a cavern begins: if you cannot swim straight up to the surface and fresh-air, you’re in an overhead environment. If the ceiling is wood or metal, chances are that you are inside a wreck, and if the ceiling is rock, you’re in a cavern.

There might be more confusion about the other end of the cavern and where exactly it turns into a cave.

The standard definition is that the primary source of light in a cavern is daylight. If you and I swim into a cavern and lose sight of the entrance and daylight, we have exited the cavern zone and entered the cave proper. And for the record, there are no caverns at night… and some cave systems do not have a cavern zone to speak of at all. (The Eagles Nest system in Florida as an example.)

That definition does not change for rebreather divers, but there is a subtle change that fundamentally sets up one of the challenging limits for overhead training on any CCR.

One absolute limiting factor for all open-circuit divers is the volume of gas they and their buddy or buddies are carrying. That volume (X litres or Y cubic feet) helps to define just how far they can travel into an overhead environment… given that they follow the established guidelines for gas volume management.

In TDI’s open-circuit (OC) cavern course, penetration is limited to one-third of the volume of a single diving cylinder or one-sixth if the divers are using double cylinders. This is somewhat further defined to explain that the available volume for penetration for the whole dive team is set by the team member with the smaller cylinder or who has the smaller(est) starting volume.

The same volume limit is suggested for OC intro-to-cave graduates.

This limit very effectively helps to “police” or control new cave divers’ return access to open-water and safety. Since running out of gas is #1 on the list of things to guarantee a cave diver is going to have a bad day, the one-third in a single / one sixth in twins guideline goes some way in keeping new cave divers from venturing too far into the cave.

But a fully functional CCR does not have the same sort of built-in restriction. Certainly both diluent and oxygen supply is limited but those limits are measured in hours rather than minutes.

Let’s take the oxygen supply as an example. (Forgive the use of SI units but cubic feet are more complicated and unnecessary to get the point across. If you are only used to American Customary Units, just think of litres as quarts.)

We’re taught that the average per minute oxygen consumption rate for a diver is 1.5 litres. This volume is depth independent. And unlike their OC breathing brother and sister divers, for a diver on CCR, it really makes little difference whether the consumption is measured on the surface or at advanced trimix depth. One’s consumption rate will vary a little with workload, but 1.5 litres makes a pretty good average to work with. For now, let’s make life simpler and a tad more conservative, and use a consumption rate of 2.0 L/min. This is really quite high, but two litres a minute makes the arithmetic even easier than it would be at 1.5.

Now the smallest rebreather tank in common use has a wet volume of about two litres. That means every full atmosphere of pressure in that tank equals two litres of gas. In other words, a fill of 200 bar means there are 200 X 2 litres of gas. That’s 400 litres of gas. Quick math… at two litres a minute consumption, this volume of gas will last up to 200 minutes!

Even if we follow a sort of rule of thirds and suggest a CCR diver only use one-third of his or her starting volume of oxygen, one third of 200 minutes is more than an hour.

This means that if a beginning CCR cave diver follows the same gas rules as an OC diver, he or she can swim into the cave for an hour before having to turn the dive on gas volume! An hour of swimming into a cave usually translates into about an hour swimming out. Sometimes the flow helps to make an exit a little shorter, but an hour would be a fair estimate.

I think even those of us who have zero cave experience will begin to see the potential for a huge problem with this scenario.

If we were to line up the special concerns of those who teach CCR cave diving, at the front of the queue would be: a rebreather is essentially a potentially wicked cross between a time machine and a gas extender. What makes it potentially wicked is that compared to the classic North Florida set of twin steel tanks (even the big ones) the most inexperienced diver can wander deeper in to a cave system… much deeper than he or she should. If something bad happens, an hour is a long swim nursing a problem.

The “magic bullet” designed to help avoid this type of event centers on bailout gas.

Bailout gas is what a CCR diver carries for contingencies. Should the rebreather become completely inoperable, then they stop using it and start breathing from a tank of compressed gas using a scuba regulator. In other words, they fall back on good old-fashioned open circuit.

Some time is spent in the foundation dives for cavern and intro-cave CCR programs working out how much bailout gas each diver must carry, and how far from the surface that gas allows them to venture.

The calculations for this distance are based on a consumption rate effected by a carbon-dioxide breakthrough on the rebreather. A breakthrough such as this would probably result in a diver breathing like a racehorse on the final furlong of the Preakness. Therefore, the calculations are conservative and the guidelines they offer for penetration are written in stone: a sensible diver would never dream of compromising his safety by ignoring these guidelines.

Is your head spinning yet?

The truth is that the task loading for a student taking a CCR Cave class is really high. In addition to the gas management “thing” they have to master all the skills expected of an OC cave diver. They have to run line, place line markers, read the cave, overcome current, learn navigation, perform lost line drills, lost buddy drills, show their instructor perfectly executed bottle swapping in zero vis, and prove they can swim without kicking up a curtain of silt. And when that’s finished, they need to come up with strategies for rebreather-specific issues. They have to run their CCR manually, in SCR mode, they have to deal with depleted diluent, low oxygen, stuck solenoids, and a raft of other “fun” challenges!

Is your head spinning now?

The truth is that I dive CCRs in caves by choice. I believe that all things being equal, a rebreather is the right tool for cave exploration eight times out of ten. (Sidemount covers the other 20 percent!) Like so many high-risk activities, the pay-off is high-value. It’s also a class I love to teach because it is such a challenge and students walk away with a justified sense of accomplishment.

Is Cave CCR the ultimate challenge in diving? I know Brian [Carney, president of TDI] and the team in TDI’s training department well, and I am sure they have other cards up their sleeve; but as it stands, I cannot think of another program that tests a diver’s mental and physical stamina more than this course.

Is it fun? Yes it is. Is it useful? Certainly. Is it tough? Sure thing. Should you start planning to challenge yourself? Well, I don’t know if you’re ready but if you think you might be… Go for it!

OK, before drilling into a few of the real benefits and surprises waiting for us when we decide on International Dive Travel, and certainly one of the most interesting associations with “foreign lands” in my diving career, we need to walk through a very quick geography lesson, followed by an equally brief history lesson!

Newfoundland is a big island off the east coast of North America. In fact, it is the most easterly point in the whole of North America and Signal Hill outside of Newfoundland’s capital St. John’s is where Marconi set-up his apparatus to receive the first radio signal sent skipping across the Atlantic from Cornwall, England in 1901. Like most of that part of the world, Newfoundland is rich in Celtic culture thanks to the influence of its early Ulster-Scot settlers, and the locals still sound more Irish than American. The waters surrounding the island are chilly (think icebergs drifting down from nearby Greenland… even in June!), are filled with the most amazing marine life — including many species of whale and are home to four of my favorite shipwrecks… anywhere in the world. We’ll get to those in a few moments.

When the Second World War erupted in Europe, Newfoundland — which today is a Canadian province — was part of Great Britain. Hence, when that country’s Prime Minister declared war on Nazi Germany in 1939, Newfoundland was automatically part of the Allied headcount. Canada followed close behind them, but it was not until a very closely fought referendum ten years later in 1949, that Newfoundland joined the Canadian Federation to become one of its ten provinces.

So, what about those wrecks? Just outside of the city of St. John’s in the middle of Conception Bay sits a small blob of land called Bell Island, and Bell Island had a very productive mine that exported iron ore to steel mills in several countries including those in Cape Breton, Canada. At the outbreak of war, these mills a little to the south in Nova Scotia, accounted for about a third of Canada’s steel production. With shipments from the Bell Island Mine to German factories cut off because of the war, it was inevitable at some point that the Germans would attempt to interrupt production and throw a “spanner in the works” for the Allied war effort. And interrupt they did.

On the night of September 4th, 1942, a German U-Boat sneaked into the anchorage at Wabana, Bell Island where ships loaded ore to be carried away to various “customers”. The next morning and within sight of the guns of the Bell Island Battery, the U-Boat sank two ore carriers moored at the loading docks: SS Saganaga and SS Lord Strathcona. Twenty-nine men were killed in the attack, all of the victims were seamen aboard the Saganaga.

The Battle of the Atlantic had suddenly come to within a few hundred metres of North America’s shoreline.

The strategic importance of the mines on Bell Island did not diminish of course, and just a couple of months after the first attack, a second U-Boat crept into Wabana and found several ore carriers at anchor.

The U-boat captain fired a torpedo at the 3000-ton Anna T. It missed and exploded ashore ripping into part of the loading dock and disturbing the sleep of many inhabitants on the island. In the next several minutes, two more torpedoes were fired at SS Rose Castle. Rose Castle sank, taking twenty-eight of her crew with her, five of whom were native Newfoundlanders. The Free French vessel PLM 27 was the second target. She sank almost as soon as a torpedo hit, taking twelve men to the bottom of the bay with her.

In the space of less than 15 minutes, two ships, several thousand tons of ore and 40 men had been lost. The U-boat escaped even though there were three allied navy escort vessels in the area.

The four Bell Island wrecks sit today at reasonable depths (the PLM 27 the shallowest at around 23 metres / 75 feet, the Rose Castle the deepest at 43 metres / 145 feet), and within a radius of a few minutes boat ride of each other and only a stone’s throw from land.

When I was first invited to dive the Bell Island wrecks, I must admit that Newfoundland seemed as remote to me as the dark side of the moon. Newfoundland was’ at least in my ignorance, nothing but folk singers, remote fishing communities, moose, and wild, wild countryside battered by strong winds and salt spray off the North Atlantic. Through a number of visits over the following few years, I discovered that it was all of this and so much more.

The wrecks were one of the first surprises. Four shipwrecks each more interesting and more crammed with history than the last. After the first handful of dives, I christened the area Truk Lagoon North. Perhaps using a little poetic license but the things that seemed common to both areas were history, the awe inspiring evidence of the destructive power of torpedoes, the sadness of the lives lost, and the contrasting beauty of the creatures that had made the wrecks their home. Like many divers, I have a fascination with WWII casualties and the story all wrecks have to tell those with time enough to listen. Like the Japanese fleet in Truk, The Bell Island wrecks are master story-tellers.

One of the best pieces of luck I had on my first visit to Newfoundland and Bell Island was meeting Rick Stanley. Rick is a proud local who owns and operates Ocean Quest Resort, which was home-base for our group during our visits. Rick is a strong advocate for all things Tourism for Newfoundland, and almost single-handedly has promoted responsible diving on the wrecks, as well as campaigning to have them designated as a war grave and a protected site. He and his staff, made our group welcome and introduced us to local hospitality… including the infamous Screeching In ceremony.

Screeching In is when visitors (people from away, is how the locals refer to tourists) are made honorary Newfoundlanders. Space prohibits a blow-by-blow account of a true Screech In ceremony but proceedings include strong rum, eating local delicacies such as cod-tongue, hard-tack (ship’s biscuit) and dried capelin (a small smelt), singing, dancing, and “kissing the cod” which really does involve getting close and personal with a large dead Atlantic Cod (gadus morhua). Having survived being “Screeched In” during several trips, I can honestly say, it is one of the most bizarre and funniest things I’ve done because of diving.

Partway through my third trip to dive the Bell Island Wrecks, Rick Stanley asked me if I would be interested in putting together a group of divers “Capable of exploring the Bell Island Mine.” Of course I said yes.

The mines were abandoned when it was no longer economically viable to operate them; but the closure was oddly abrupt.

The mines on Bell Island opened for commercial mining in late 19th century and were once the world’s largest submarine iron ore mine with passages occupying an area under the seabed of Conception Bay roughly five kilometers by five kilometers or approximately nine square miles in size.

The mine that Rick was interested in having surveyed and accessed — and that was the project’s main aim — had been closed since Christmas 1949. The story goes that the workers downed tools for the holiday and were never allowed back into the workings.

Rick and the Bell Island Historical Society were curious to have a team of divers explore the mine system — or as much of it as practical in the 12 days available — and look for evidence of cave-in, collapse, artifacts and other things that might interest a different type of visitor than the ones currently coming to the mine museum sitting at the old entrance to Mine Shaft Two.

The questions they wanted answers to where simple: can it be dived? Is it interesting enough to attract divers? Are conditions supportable for regular visitors? There were some side issues that needed to be addressed, but the hope was to open up a unique form of adventure tourism for the island and its economy. With a background in Tourism Marketing, I was certainly curious enough to take Rick up on his offer and set about building a team that would be able to pull things off. After a simple exploratory dive in July of 2006, we set a target date for the following January/February, and started planning.

Our goal was to investigate as much of the inundated mine as practical within the short time available. We knew the water would be cold, and because of the surface support needed, we also knew that our efforts would have to be focused on a time when normal tourist activity would not interfere; and that meant winter which also would be cold.

I was lucky to find the perfect group of men and women who were not daunted by the challenges that the season, the logistics, and the challenging dive site would present to us.

Newfoundland in the heart of winter is an interesting study. Stuck as it is with both feet in the Northern Atlantic, and its face weather-beaten by winds coming off the glaciers of Greenland or Labrador, it is not for the faint-hearted. Several of the team where Brits whose experience with a real Canadian winter had been limited to movies and books, got to experience a true winter storm on arrival and several of us had plane delays getting into St John’s airport. My plane was almost on the runway but the pilot aborted and we headed back to Halifax International with our tail between our legs and our hearts in our mouths.

But eventually, all 16 of us were together in the lounge at Ocean Quest Resort, sorting gear, knotting line, and pumping gas.

During the following two weeks, the team surveyed the mine looking for any evidence of cave-in or collapse in the mine shaft and laid permanent guidelines from the surface along the main shaft to a depth of approximately 30 metres. The seam of iron ore slopped at an angle of approximately ten degrees and continued many thousands of metres under the overlay of ocean floor below Conception Bay. In addition to the main line, four ‘jump lines’ were laid in side passages. The initial plan was to extend these side passages (roughly horizontal) approximately 300 metres east and west of the main shaft. Overall a total of 2km of line was laid in the mine.

The search for artifacts left behind when the mine was abandoned turned up mine equipment, personal effects such as lunch boxes, and we discovered graffiti, drawn by the miners using the soot from their carbide lamps. The system was mapped sufficiently to enable the conclusion that the mine would make a challenging diving destination for cave divers to explore.

Every overhead environment presents divers with a number of challenges well beyond the scope of recreational diving. As well as the obvious threats to the team’s well-being — gas management, navigation, light, depth and the cold — the health of one of our team played a role. On Sunday, February 4, Joe Steffen, well-known in the diving communities in both the Great Lakes and North Florida, suffered a massive embolism and died. Joe perished in a few metres of water just a couple of minutes from the surface operations. Ironically “Iron Man” had an undiagnosed problem with his lungs which did not show up during a medical he’d had before joining the team from his home in Ohio, and attempts to revive him at the dive site and the medical facility adjacent to the mine were unsuccessful.

We lost a great buddy, and Joe — a career police office — left behind a wife and young son, and many, many friends.

In consultations with the various sponsors — which included TDI, Fourth Element, Whites, the NACD, and Ocean Quest — as well as local authorities, the exploration of the Bell Island Mine continued and its success was dedicated to Joe’s memory.

The following year, Joe’s widow, Jennifer, visited Bell Island for a memorial service which included two of the team (Mike Fowler and Steve Lewis) placing a memorial plaque and an urn containing Joe’s ashes in the main shaft of Bell Island Mine No. 2.

Tourists continue to visit the Mine and divers enjoy the four wrecks that sit above its vast network of passages, but underwater operations at the mine await further work.

Imagine a laser light show at a Pink Floyd concert and place that image underwater. Picture light beams piercing through the water lighting up the bottom contour. You may or may not have “Shine On” stuck inside your head but you’re certainly seeing the cavern light up in front of your eyes. It’s not just the light show that attracts people to dive caverns; the visibility, natural formations, and skills associated with this type of environment lures in divers every day.

As divers, we often ask each other “How was the vis?” Rarely can we answer; “as far as the eye could see!” A cavern is not the environment you’re going to find waves that stir up the bottom. Any present water movement in and around many caverns worldwide typically pulls any present sediment away allowing for limitless visibility. Diving in the clear water of caverns allows one to feel like they are gliding through midair. You don’t have to search for that great “vis” when you can find it in the unexpected realm of cavern diving.

As a TDI Cavern Diver, you have the opportunity to get a “sneak peak” of the underwater realm inside of the earth. Within the limitations of your cavern training (ie; remain within the natural light zone, no farther than 200 linear feet from the surface, no restrictions and more) you have a plethora of new things to see while diving in this environment. Caverns around the world have visible fossils, stalagmites, stalactites and rock formations you typically cannot find in the open ocean. Taking the TDI Cavern Diver course is a great way to try something different and see something new.

You might be wondering, what is involved in the TDI Cavern Diver course? The objective of this course is to train divers in the proper planning, procedures, techniques and hazards of diving in caverns and the overhead environments. If you are over the age of 18 (15 with parental consent), can show proof of a SDI Open Water Scuba Diver certification or equivalent, and provide proof of a minimum of 25 logged dives, you meet the prerequisites for the program. During the TDI Cavern Diver course you will learn new swimming techniques by fine tuning your body posture / trim, buoyancy control and learn how to properly deploy and follow a guideline. Have you ever seen people in the water that make diving look so effortless? By fine tuning your diving techniques you can get closer to becoming one of those divers.

Contact SDI TDI and ERDI
If you would like more information, please contact our World Headquarters or your Regional Office.

“More than 300 divers – including open water instructors — have died in caves just like this one. Prevent your death. Go no further.”

Now, I can’t speak for anyone but myself, but when I was a fledgling open water diver, if faced with a sign that shared that little snippet of information with me, I am pretty sure that I would have turned around and gotten the heck out of dodge. Big signs with that wording and an image of the Grim Reaper are placed at the entrance to most caves in Florida as well as other spots in the Bahamas, Mexico and so on. But sadly, many divers, divers who have no business being in any overhead environment and especially a cave, choose to ignore them.

The question is why?

If you take a look through the standards for SDI’s open-water programs – from beginner to open-water instructor trainer – there are some very specific recommendations to stay away from “overhead environments.” For the record, an overhead environment is ANY spot from which a direct ascent to the surface is not possible. And to further clarify, a direct ascent means that if a diver were to fill a lift bag, DSMB, or balloon at depth and release it, it should make it to the surface without touching rock, wreck, coral or anything else. If that lift bag, DSMB, or balloon DOES touch anything at all, the diver should be trained and equipped, to be there.

OK, more definitions. It’s fair to say that the foundation of most of the skills, techniques and gear associated with technical diving have their beginnings in cave diving. Cave diving is – to many – where sport diving stops and technical diving begins. Certainly, courses in cave diving from TDI are considered “Fully technical” and for good reason.

Since the inception of structured cave diving education, the progress from being an experienced open-water diver to a full cave diver has followed a similar pathway regardless of the certifying agency or location of the program being offered.

It begins with a cavern course. This program is designed to introduce basic skills such as how to swim without kicking up a huge cloud of silt; how to use a reel and deploy a line in water without getting tied up like a Christmas present; how to communicate with your buddy so there’s no ambiguity; and how to manage gas volume so that you and your mate have something to breathe for the duration of the dive even if something goes totally pear-shaped and one of you loses all his gas.

The next step in cave diver training is an Intro-to-Cave class. This builds on the fundamental skills presented in the cavern class and introduces more intensive equipment management drills. Graduates from this level of training can venture into the cave, but still have to function within certain limits, such as staying in the main passageways and making no jumps to side passages.

And finally is a full-cave class which essentially gives a diver a “licence to learn,” inside the cave proper and its off-shoots and side tunnels. But even then, there are limits and several other steps in both experience and training before this diver has “free-run” of the cave.

NONE of the skills required to help keep a diver safe in a cave or cavern are taught in a recreational open-water class… including an instructor class… and the equipment used by sport divers the world over has no place in a cave.

Caves can be beautiful but that beauty can become extremely ugly in a couple of heartbeats. Here are some things that have happened to untrained divers who almost died in a cavern or cave but somehow managed to find their way out.

“We only intended to swim in a little way, but there were lots of passages and we got turned around…”
“The water was really clear but my buddy crashed into the bottom and I lost sight of him and the exit. I think he is still in there…”
“We had a light between us but it went out. It was really dark and I kept swimming into the walls…
“I swum in a little way and then my octo started to freeflow…”
“We followed a line and it just stopped and then I got tangled in it…”
“I panicked when I turned and could not see the exit.”

Let’s look again at some definitions. The definition of a cavern, and the limit of a cavern dive, is that the primary light is sunlight. Cavern divers must still use and carry lights (several of them), but at all times, both divers must be able to see the exit of the cavern. And for the record, the Grim Reaper sign mentioned in the first paragraph is usually placed at the edge of the so-called cavern-zone… the transition point from cavern to cave.

Now, just in case you are thinking to yourself right now: “Well, I guess it’s OK to go and take a peek inside a cavern because the sign telling me to go no further is there and NOT at the entrance to the cavern itself” let’s consider a couple of things including the benefits and reasons behind the skills taught cavern divers.

Remember the first rule of scuba diving: Never hold your breath? Well, the first rule of technical diving delivers more or less the same message: “Always have something to breathe!” That way, you never HAVE to hold your breath and break the first rule of scuba diving.” That makes sense doesn’t it?

Many of the several hundred divers who have perished in caves have actually died in the cavern zone: right there within sight of the exit. How, you might ask, could that happen? After all, it’s just a cavern, nothing challenging about that! Well, as surprising as it may seem, they ran out of something to breathe because they could not see daylight. They had flutter-kicked their way a few metres into the cavern and in doing so had totally silted things out so badly that they were suddenly in a black-out. They found themselves lost! Then, with their breathing rate elevated because of stress… and then panic… they had used up their air supply in minutes while searching for the way out. In their confusion, some had actually swum further into the cave.

Occasionally, the poor sap who ends up dead may have been told that caverns and caves are safe, and believed it. There may even have been an open-water instructor telling them that it’s OK to follow them into a cavern or cave. Well, the truth is that is in NOT OK and dive leaders who take untrained divers into an overhead are breaking standards… pure and simple.

There are no grey areas when it comes to this overhead stuff. Going in there without the right kit and training is seriously tempting fate, and there are so many other ways to enjoy yourself with scuba. Please, please, do not go into an overhead until you get training in overhead diving and get yourself some serious kit and gain the experience to use it properly.

Steve Lewis
TDI instructor trainer #6

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If you would like more information, please contact our World Headquarters or your Regional Office.

Isn’t it time you learned more?

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Perhaps one of the most common questions Technical Diving International’s (TDI) Training Department gets is “why do I need training for overhead environments?” While this question seems pretty obvious to TDI, we understand why it is not so obvious to the average diver. After all, you are breathing underwater, controlling your buoyancy and managing air just like you would on any other dive, right? Wrong. In this article we are going to focus on one specific type of overhead diving: caves.

Caves are one of the most fascinating environments a person can explore. Just think about it: these massive natural tunnels (some only a metre or 3 feet down) are below us, some dry some wet, while life on the surface moves along at its normal pace completely unaware that they even exist. These natural tunnels are responsible for a large portion of our drinking water and for moving water to the oceans or lakes to avoid flooding during rainy seasons and snow melt. Nearly every continent and country contains caves, most undocumented and unexplored. Some of these caves are just barely big enough for an adult to fit though while others are big enough to fit a descent sized town in.

While caves are undoubtedly fascinating, and there is clearly a need for them to be explored, they deserve a lot of respect and require specialized training before they are entered. Not all caves are made alike; some caves are low visibility with high water flow while others have clear warm water. Some caves are solid with no chance of the “roof” collapsing while others have what are called “breakdown rooms.” These rooms are where the earth above has been eroded to a point where it falls to the floor of the cave forming a large cone in the center; when this roof will fall is anyone’s guess. In some areas, even the caves that appear to be very stable are subject to seismic activity and could collapse.

The point here is that before entering any cave system proper training is required. Your TDI instructor, among other knowledge and skills, will teach you how the cave was formed and its stability. You will also learn things to look out for when planning a cave dive like “where do I look to find recent seismic activity so I know when it is safe to dive?”

Cave training is also a progression in training starting with caverns where you learn the basic techniques for deploying guidelines, buddy communication with lights and air management, all while staying in the ambient light zone. The next course is cave which takes you beyond the ambient light zone further into the cave requiring more air management skills and guideline techniques. The pinnacle of cave training is full cave; here you will learn complex circuits with jumps off the mainline and even more air management to allow for decompression dives. Please note: Decompression procedures is a pre-requisite for this course, decompression diving is not taught as part of the full cave course.

At any stage of your cave training you can add in other training such as: cave- diver propulsion vehicle (DPV), cave survey, sidemount or sump diving. There is a lot to do, see and learn just below the surface of the rock we walk on every day, but it requires some training from a TDI Professional. After this training you will be amazed at the exploration you will be capable of, and your friends will love the stories of your adventures.

So if cave diving is something you would like to learn more about, ask your local TDI facility or Instructor for more information. Our website is always a great place to start for additional information https://www.tdisdi.com, or simply give us a call at 888.778.9073 or 207.729.4201.